The present invention relates to a structure of a thin film magnetic head provided with a coil whose electrostatic capacitance is the same on both sides of its center tap.
For use in recording or reading in electronic computers or acoustic devices, a magnetic head having a center tap has the advantages of easy switching from writing to reading or vice versa and a very easy selection of tracks by means of an X-Y switch in comparison with a two-terminal magnetic head. The two-terminal head can be used as a center-tapped magnetic head by being provided with an additional pulse transformer with three terminals on the primary side. The use of the additional pulse transformer is not, however, preferable because it makes the magnetic head bulky.
There is a wide track width magnetic head using a magnetic core in which a coil is wound with a double-stranded wire and a center tap is derived from the connection portion of the double-stranded wire. Such a magnetic head has the drawback that a plurality of the thus bulky magnetic heads cannot be formed on one substrate because of their large bulk. There is, therefore, a proposal in which the magnetic head should be formed by thin films for improvement in track density.
In U.S. Pat. No. 3,344,237, for example, there is disclosed a magnetic head having one-turn coil, which, however, requires a large amplification circuit because of its small input and output signals, and it is not possible to make smaller one as desired. German Layed-Open Patent Specification DOS No. 2,052,642, on the other hand, discloses a thin film magnetic head having a coil with plural winding turns, which employs a structure that the coils are expanding in proportion to the number of turn so that conductors may not overlap on the substrate, and thus has the drawback that it cannot form high-density magnetic heads. In such a magnetic head having a coil with its center tap derived from a central winding, the coil is different in inductance and in electrostatic capacitance depending upon whether it is on one side or the other of the center tap with the result that equalization can not be provided if we were not made fine adjustment to the amplifier circuit. This, therefore, leads to the new addition of inductances and capacitors to the circuit. The coil having the above-mentioned structure, for example, has a drawback that the inductance and electrostatic capacitance of one section of the coil is more than three times as great as that of the other section of the coil even if it has only several winding turns on each section.
Another example is shown in IEEE Transactions on Magnetics; Vol, Mag. 9, No. 3, (September 1973) P 322, in which a magnetic head has a coil with a center tap. The coil is wound in the same pattern as the first layer and the center tap is derived from the central turn of the windings. The head is formed by a mask evaporation method. In the ordinary mask evaporation method, however, a precise pattern cannot be obtained because films may not be deposited in a correct pattern as the mask. The inaccuracy, on the other hand, eliminates the danger of defective insulation or conduction on overlapping portions because deposited layers define a gentle inclination at their edge. If the head is desired to be formed in high density and in a correct pattern, then it must be formed by etching technique using a photomask. The formation of a magnetic head having the structure described in IEEE Transaction on Magnetics by the etching technique using the photomask requires the using which cannot aboid to step up the etched pattern. This produces many defects at this step, and permits no industrial manufacture of the head having such a structure.
If a magnetic head is intended to be manufactured with more precision and in higher density, then research must be made for pattern and structure suitably adapted for manufacturing process.